The invention relates to a drilling device with an impact-rotation tool producing drill holes in masonry consisting of aerated concrete or similar material. In operation, the impact rotation tool is clamped in an impact drilling machine or similar apparatus.
Drilling devices are known, in which, in particular to produce drill holes in aerated concrete or similar material, an impact shank is used instead of a drill bit. This impact shank is driven into the aerated concrete and thereby produces an exactly defined drill hole, the aerated concrete being compacted in the region of the drill hole at the same time. These known devices have the disadvantage that the impact shank becomes jammed in the drill hole and thus can be removed from it only with difficulty or not at all.
It is also known to use a rotary shank instead of a drill bit. When preparing the drill hole in aerated concrete or similar material the aerated concrete is compacted and displaced in the region of the drill hole. Rotary shanks disadvantageously widen the drill hole. In particular, the rotary movements carried out during the drilling operation in dry aerated concrete lead to the drill hole being reamed out. When producing corresponding drill holes in wet aerated concrete on the other hand, it happens frequently that a fixing plug cannot be inserted in the drill hole, since the latter is too small in comparison with the diameter of the fixing plug. Owing to the low strength of aerated concrete, however, relatively large diameters have to be used for approved fixing plugs to introduce the load. These fixing plugs are not suitable, however, for through mounting. On the other hand, expansible plugs with a relatively small degree of expansion cannot be used in aerated concrete since, when preparing the drill hole, the drill hole is widened through slight deviations from the drilling axis, resulting in the holding value of the fixing plug to be inserted being impaired.
The invention is based on the problem of producing a drilling device to prepare geometrically exactly defined drill holes in aerated concrete or similar material, which moreover permits the drilling device to be removed without difficulty from the drill hole, when the drilling operation has been completed.
According to the invention the drilling device includes an impact-rotation tool consisting of an impact-drilling shank, a carrier bush connected to the impact-drilling shank and a ram lying within the carrier bush. The ram is provided with a drill-bit like locating means for engagement in an impact drilling machine. In operation of the impact drilling machine, the ram with its drill bit-like locating means disengages from the carrier bush, when the impact drilling machine is switched on and drives the impact-drilling shank into the aerated concrete as a result of the impact energy produced by the impact drilling machine. As a result of the friction between the impact-drilling shank and the aerated concrete, rotation of the impact-drilling shank with the ram is prevented during the drilling of the hole, so that during the drilling operation it is only the ram mounted with clearance in the carrier bush that rotates. Through the advancement of the impact-drilling shank during the drilling operation, without this itself rotating, a reproduction of the shank in the form of an exactly defined drill hole is formed in the aerated concrete. Slight axial deviations during the drilling operation are accommodated by the play existing between the ram and the carrier bush. Larger deviations are not accommodated by alterations in the geometry of the drill hole itself, but are averted by the transverse force occurring in the aerated concrete on the impact-drilling shank, without which there would be a change in the drill hole.
When the required drill hole depth has been reached, the aerated concrete is compacted and displaced in the area of the impact-drilling shank introduced into it. The impact-drilling shank is prevented from becoming jammed in the compacted aerated concrete as the impact-drilling shank is being removed, since, as the impact-drilling shank is withdrawn from the drill hole, the ram becomes fixed in the conically formed carrier bush and thus the rotary movement of the ram is transferred by the carrier bush to the impact-drilling shank itself. The impact-drilling shank can therefore be removed from the drill hole without further force being applied.
An especially advantageous development of the invention provides for the impact-drilling shank to have a notch at its end opposite the end adjacent the ram, i.e. the end which engages the aerated concrete when drilling the hole. An additional safeguard against rotation of the impact-drilling shank as it is being driven into the aerated concrete is achieved by this shaping of the shank tip of the drilling device according to the invention.
A cylindrical portion is provided on the impact-drilling shank and has an increased diameter relative to the remainder of the shank. This increased diameter of the cylindrical portion of the shank in this region corresponds to the diameter of the fixing plug to be inserted subsequently in to the drill hole. By this means it is possible to obtain a drill hole of exact definition in this region, matched to the fixing plug to be inserted.
The conical shaping of the leading region of the leading region of the impact-drilling shank, which at the front end of the impact-drilling shank has a diameter of about 0.9.times.the nominal diameter of the fixing plug, facilitates the later removal of the impact-drilling shank from the drill hole, since a reduced friction with the wall of the drill hole is achieved by this.